Rotor blade



United States Patent O 3,105,557 ROTOR BLADE Voorhis Frederick Wigal,600 Mobile Ave., Jackson, Tenn. Filed Aug. 4, 1960, Ser. No. 47,546 17Claims. (Cl. 170-159) T-his invention yrelates to airfoil elements ingeneral, and in particular to a rotor blade of the type used in lift andsustension of helicopters and the like aircraft, although it is notlimited to such use.

The rotors in actual use may be characterized in four main classes, asfollows:

(a) Laminated wood built around a metal spar.

(b) Small, wing-type ribs, spaced closely around a metal spar, andcovered with fabric or aluminum sheet.

(c) Aluminum or fabric covering over shaped wood, cellular .plastic orhoney-comb filler, built around a metal spar.

(d) Some arrangement of extruded aluminum sections which may or may nothave :the spar as an integral part.

All of these types involve slow and laborious processes in the making,demand a high degree of craftsmanship, and entail high cost in thefinished product.

It is therefore a principal object of the present invention to simplifythe manufacture and reduce the cost of rotor blades. Another object isto achieve a proper airfoil section without the need for hand-finishingoperations. A still further object is to provide a balanced bladewithout resort to protruding, external weight additions. Other objectsinclude easy reproducibility of blades having proper balance andsection, and the attainment of high strength and flexibility with lowweight.

These and other objects are attained by the present invention, which maybe briefly described as a blade built up along its length from la seriesof plastic units of airfoil section arranged in side-:by-side, relation,each unit consisting of an upper shell and a lower shell withstiftening, internal ribs, and secured on a plastic-lled, multitubularspar running the -length of the blade.

For a more detailed description of the invention, reference is made tothe following specification, as illustrated in the drawing, in which:

FIGURE 1 is a top view of a rotor, foreshortened by removal of anintermeditae portion,

FIGURE 2 is an enlarged sectional view taken on the line 2 2 of FIGURE1,

FIGURE 3 is an internal View of one of the halves of the airfoil shell,as seen along the line 3 3 of FIGURE 2, with the spar tubes removed,

FIGURE 4 is an enlarged, sectional view taken on the line 4 4 of FIGURE1,

FIGURE 5 is an enlarged, sectional view taken on the line 5 5 of FIGURE1,

FIGURE 6 is an enlarged, sectional view taken on the line 6 6 of FIGURE1,

FIGURE 7 is an enlarged, sectional view taken on the line 7 7 of FIGURE1,

FIGURE 8 is a sectional view taken on the line 8 8 of FIGURE 7, showingthe spar element of FIGURE l without the surrounding, airfoil shell, and

FIGURE 9 is an axial section of a spar tube, showing an operation offilling the tube with plastic-impregnated reinforcing filaments.

Referring to the drawings by characters -of reference, there is shown arotor blade built around a spar, indicated generally by the numeral 1,which constitutes the backbone of the blade, and as such chiey providesthe mechanical strength of the system, as against bending ice stressesfor instance. In one feature of novelty of the invention, later to bediscussed, the spar is constituted by a series of tangentially united,tubular elements. In the embodiment shown, these are three in number,with a central tube 2, flanked on opposite sides by a pair of outertubes 3 and 4. The middle tube 2 should be centered on the pitch axis ofthe blade. This tube which is also preferably located at or near thepoint of maximum thickness of the airfoil is of a diameter to take fulladvantage of the available space within the airfoil, and consequentlythe outer tubes 3, 4 are of a lesser diameter than tube 2 due toconvergence of the vairfoil Walls or shells.

The airfoil shell, which is carried by the spar, as a covering mantle,is made up of a series of identical sections, each of which is indicatedby the numeral 6 in FIGURE 1, land which is shown in detail in FIGURES 2to 6. Thus, in FIGURE 2, it is seen that the airfoil is made up by apair of identical, molded plastic shell halves having a skin 8 ofairfoil contour, and a series of internal, stiffening ribs 10 and 12.Defining the central plane of the complete airfoil, each'shell halfhas aforward flat region 14, a rearward flatregion 16 and two pairs oftransverse fbosses 18 and 19 lying on respective sides of the spar 1.Ribs 10 and 12 have a generally similar profile throughout most of theirlengths, but as seen in FIGURE 2, the ribs 12 have an extra, inwardsweep in the neighborhood of the bosses to give added bracing thereto.The bosses 18 are also braced in the longitudinal direction of the rotorblade by ribs 20. In the region forward of the bosses 18, the ribs 10and 12 are provided with suitable, arcuate recesses 21 to snugly receivethe spar tubes 2, 3 and 4. As shown, the tubes are welded together, Ibutthe system-may be fabricated in other ways, as by extruding in the formof a three-part tube, or by pressure deformation from a single, largetube. Preferably, the spar will consist of high strength aluminum orother light metal of suitable strength.

For quick, accurate and durable assembly, the airfoil units 6 areprovided with integral dowelling elements alternately arranged so thatthe shell half may be used on either side of the airfoil. Thus, inFIGURE 3, the hat region of join, 14, has alternately occurring pins 22and recesses 24. It will be seen that when a shell half is grought intomating relationship with another identical half, being thus turnedthrough a angle, the pins of one will engage in the recesses of theother. Similarly, in the region of join, 16, at the trailing edge of theairfoil, alternately arranged holes 26 and pins 28 are provided.

With the shell halves accurately spotted by the mating pins and holes toproduce the complete airfoil, the assembly of the unit is secured |bymeans of four screws 30 cooperating with axial bores in the bosses 18,19. As seen in FIGURES 1 and 2, the arrangement is such that two of thescrews are applied from each side of the airfoil, and the screw heads oneach side are diagonally disposed. Thus, each shell -unit (FIGURE 3)will have threaded bores in the lower left hand boss and in the upperright hand boss, the other two bosses having bores sufficient to .passthe screw shank. The outer side of the shell is provided with suitablecountersinks for the screw heads. This arrangement of screws is not onlyconsonant with the principle of using identical half-sectionsthroughout, but also maintains proper. balance on both sides of theairfoil and throughout its length.

In order to provide la smooth, unbroken expanse of airfoil surface, theinternal edges of the shell segments are arranged for overlappingengagement. As seen in FIG- URES 3 and 4, the extreme leftward rib lllis located slightly inwardly of the edge of the shell to provide amarginal strip 32 wherein the thickness of the skin 8 is reduced byone-half. Correspondingly, the shell extends slightly beyond the extremerightward rib to provide a marginal strip 34 which is rabbeted from theouter surface of the ainfoil to a depth of half the thickness of theshell whereby to overlap the marginal strip 32 of an adjacent section 6to provide a neat joint. The lap joint may be secured by a suitableycement or by yapplication of V-a solvent. The use of butt joints isalso contemplated.

The outer Vend of the rotor blade may be closed by a suitable cap 36, ofmaterial similar to that of the shell segments, which can be fu-ntherutilized .to hold the Iairfoil sections in place by welding or bolting,and/ or chemically bonding the cap to the spar, as well as to theoutermost shell segment.

Any suitable means may be employed for attaching the blade to a rotorhub. For purposes of general illustration, the drawing shows a pair ofaluminum sections 36 shaped to receive the spar I and clamped thereon bymeans of screws 38. This constitutes -a block providing suicient bodyfor lany conventional coupling or attaching means.

In an important feature of the invention, the hollow tubes of the sparare loaded with ia filler to provide strength -with'out undue weight,and in a prefenred embodiment, resin-impregnated fiberglass hlaments areintroduced into the tubes and cured in place. As seen in FIGURE 9, theloading of a tube is conveniently accomplished by drawing a looped skeinof fibers 40, or roving as it is called, by means of a steel wire 42engaged in the loop. The loading operation is facilitated by means of afunnel 44 received 'on the charging end of the tube. The fibers enterunder high compression across the diametral direction land provide aclosely packed mass which is subjected to cure, when in place.

As seen in FIGURES l and 8, the extent of loading of the fiberglass lleris different in the respective tubes. Only .tube 3, the one nearest theleading edge of the `airfoil needs to Ibe reinforced throughout itsentire length. At the root end of the blade, near the rotor hub, wherethe greatest strength is needed, all of the tubes are reinforced, butinthe middle tube 2, the lling stops considerably short of that in theforward tube, as at 48, and in the rearmost tube the terminus 50 of thefiller is still closer to the rotor hub. Not only does this arrangementprovide the required strength with minimum Weight, but also enables afine :adjustment of rotor blade balance without the objectionable use ofprotruding auxiliary weights :as practiced in the prior art.

For the material of the airfoil shell sections it is preerred to useplastic Vof very tough but high impact material, such as polyamides,yacetal, or polycarbonates, and the Y impregnating material for thelglass fibers will preferably comprise a polyester or epoxy.

In the use of the invention for rotor blades, there is a distinctadvantage in that a single form of mold cavity is adequate. This is sobecause rotor blades are commonly symmetrical, with the same curvatureon the top as on the bottom, due to the need for maintaining the centerof pressure at a given point during constant changes in the yangle ofattack. However, even if a non-symmetrical Iblade is contemplated, onlytwo mold forms will Abe required.

The advantages of the invention may be summarized as follows:

(l) The Vmolded plastic shells, establish, ab initio, the

proper curvature for the `airfoil section.

(12) The parts are molded to t correctly together, so that no handfinishing is required. This makes for simple 'and economical assembly.

(3) Since `all parts are molded in the same cavity they will all be veryclosely the same Weight, and there will be no balance problem in matchedblades.

(4) impregnated, fiberglass reinforced spar gives high strength andexibility with low weight.

(5) In `a spar with separate, tubular sections,chordwise balance can beadjusted by the extent of filling in the respective tubes, thusobviating the use of external weights, which impair rotor eiciency.

While certain preferred embodiments have been shown and described, theseare not intended as limiting since various changes, modifications andsubstitution of equivalents, for instance, will suggest themselves tothose skilled in the art, in the light of this disclosure, and theinvention should not, therefore be :deemed as limited except insofar asshall appear from the spirit and scope of the appended claims.

I claim:

il. An airfoil comprising a multi-tubular reinforcing spar having acentral tube and `at least one tube on each side of said central tube oflesser diameter than said Central tube, ya ller of cured,resin-impregnated fiberglass in said tubes extending from `a common endof said tubes and terminating at progressively increasing distances insuccessive tubes, and a covering shell of symmetrical airfoil formenclosing said spar, said shell comprising identical sections of moldedplastic arranged in side-by-side relation along the length of 4saidspar, each said section comprising identical halves, each halfcomprising a wall of airfoil fOr-m, said wa-ll having ilat regions onthe axis of symmetry of the complete airfoil, lat the leading edge,

at the trailing edge and at points intermediate the said edges, dowelmeans in the said at regions at said edges, said regions at saidintermediate points lying on opposite sides of said spar and havingthreaded bores for fastening screws, ribs on the inner side of said wallextending 4from trailing edge to leading edge, and having recessesaccommodating said spar, the respective, lateral edges of said wallbeing rabbeted from the front and rear, respectively, of said wallwhereby to provide lap joints between adjacent halves along each side ofsaid airfoil.

2. An airfoil .comprising .a multi-tubular reinforcing spar having acentral tube and at least one tube on each side of said central tube oflesser diameter than said central tube, 'a filler of cured,resin-impregnated fiberglass in said tubes extending from a common endof said tubes and terminating 'at progressively increasing distances insuccessive tubes, and `a covering shell of symmetrical airfoil formenclosing said spar, said shell comprising identical sections of moldedplastic arranged in side-by-side relation along the length of said spar,each said section comprising identical halves, each half lcomprising awall of airfoil form, said wall having iiat regions on the axis ofsymmetry of .the complete airfoil at the leading edge, at the trailingedge, and at points intermediate the said edges, said regions at saidintenmediate points lying on opposite sides of said spar and havingthreaded bores for fastening screws, ribs on the inner side of said wallextending from trailing edge to leading edge `and having recessesaccommodating said spar, the respective, lateral edges of said wallbeing rabbeted from the front .and rear, respectively, of said wallwhereby to provide lap joints `between adjacent halves along each sideof said airfoil.

3. An airfoil comprising a multi-tubular reinforcing spar having acentral tube and `at least one tube on each side of said central tube oflesser diameter than said central tube, a ller of cured,resin-impregnated fiberglass in said tubes extending from a common endof said tubes and terminating at progressively increasing distances insuccessive tubes, and a covering shell of symmetrical airfoil formenclosing said spar, said shell comprising identical sections o-f moldedplastic arranged in side-rbyj side relation along the length of saidspar, each said section comprising identical halves, secured together,each half comprising ya wall of airfoil form, `said lwall having atregions on the axis of symmetry of the complete air,- foil at theleading edge and at the trai-ling edge, and ribs extending between saidedges and 'having recesses receiving said spar, the respective, lateraledges of said Wall being rabbeted from the front and rear, respectively,of

said wall `whereby to provide lap joints Ebetween adjacent halves alongeach side of said airfoil.

4. An airfoil comprising a multi-tubular reinforcing spar having acentral tube and at least `one tube on each side of said central tube oflesser diameter than said central tube, a iiller of cured,resin-impregnated fiberglass in said tubes extending from a common endof said tubes and terminating at progressively increasing distances insuccessive tubes, and a covering shell of symmetrical airfoil formenclosing said spar, said shell comprising identical sections of moldedplastic arranged in side-by-side relation along the length of said spar,each said section comprising identical halves secured together, eachhalf comprising a wall of yairfoil form, ribs on the interior of saidwall extending from the trailing edge to the leading edge and havingrecesses receiving said spar, the respective, lateral edges of said wallbeing rabbeted from the front and rear, respectively, of said wallwhereby to provide lap joints between adjacent halves along each side ofsaid airfoil.

5. An airfoil comprising a multi-tubular reinforcing spar having acentral tube and at least one tube on at least one side of said centraltube of lesser diameter than said central tube, a iller `of cured,resin-impregnated riberglass in said tubes extending from a common endof said tubes tand terminating at progressively increasing distances insuccessive tubes, and :a covering shell of symmetrical airfoil formenclosing Said spar, said shell cornprising identical sections of moldedplastic `arranged in side-by-side relation along the length of saidspar, with overlapping edges, each said section comprising identicalhalves secured together, each half comprising a wall of airfoil form,and ribs on the interior of said Wall extending from the trailing edgesto the leading edge and having recesses receiving said spar.

6. An airfoil comprising a multi-tubular reinforcing spar having acent-ral tube yand at least one tube on lat least one side of saidcentral tube of lesser diameter than said central tube, a filler ofcured, resin-impregnated fiberglass in said tubes extending from acommon end of said tubes and terminating at progressively increasingdistances in successive tubes, and a covering shell of symmetricalairfoil form enclosing said spar, said shell comprising identicalsections of molded plastic arranged in side-by-side relation along the-length `of said spar, each said section comprising identical halvessecured together, each half comprising a wall of lairfoil form, and ribson the interior of said -wall extending from the trailing edge to theleading edge and having recesses receiving said spar.

7. An airfoil comprising a multi-tubular reinforcing spar having :acentral tube and at least one tube on at least one side of said centraltube of lesser diameter than said central tube, a filler of plasticmaterial in said tubes extending from a common end of said tubes andterminating at progressively increasing distances in successive tubes,and a covering shell of symmetrical airfoil form enclosing said spar,said shell comprising identical sections lof molded plastic arranged inside-by-side relation along the length of said spar, each said sectioncomprising identical halves secured together, each half comprising awall of airfoil form, and ribs on the interior of said wall extendingfrom the trailing edge to the leading edge.

8. An airfoil comprising a multi-tubular reinforcing spar having acentral tube and at least one tube on at least one side of said centraltube of lesser diameter than said central tube, a ller `of plasticmaterial in said tubes extending from a common end of said tubes andterminating at progressively increasing distances in successive tubes,and a covering shell of symmetrical airfoil form enclosing said spar,said shell comprising identical sections arranged in side-'by-siderelation along the length of said spar, each said section comprisingidentical halves secu-red together, each half comprising a wall ofairfoil zform, and ribs on the interior of said wall transverse to saidspar.

9. An airfoil comprising a reinforcing spar having a plurality oflongitudinal passages, a iiller of plastic material in said passagesextending Ifrom a common end of said passages .and terminating atprogressively increasing distances in successive passages, and acovering shell of symmetrical Iairfoil form enclosing said spar, saidshell comprising identical sections arranged in side-by-side relationalong the length of said spar, each said section comprising identicalhalves secured together, each half comprising a wall of airfoil form,and ribs on the interior of said Wall transverse to said spar.

10. An airfoilcomprising a reinforcing spar having a plurality oflongitudinal passages, a filler of plastic material in said passages,:extending from one end yof said spar `and terminating at progressivelyincreasing distances in successive passages, and a covering shell ofsymmetrical airfoil form enclosing said spar, said shell comprisingidentical sections arranged in side-by-side relation along the length ofsaid spar, each said section comprising identical halves securedtogether, each half comprising a wall of airfoil form.

11. An airfoil comprising a reinforcing spar having a plurality oflongitudinal passages, a filler of plastic material in said passages,extending Ifrom one end of said spar land terminating at progressivelyincreasing distances in successive passages, and :a covering shell ofairfoil form enclosing said spar, said shell comprising identicalsections arranged in side-by-side relation along the length of saidspar, each said section comprising an upper and lower airfoil wallsecured together.

12. An airfoil comprising a reinforcing spar having a plurality oflongitudinal passages, a iiller of plastic m-aterial in varying amountscontained in the respective passages, and a covering shell of airfoilform enclosing said spar, said shell comprising identical sectionsarranged in side-by-side relation along the length of said spar, eachsaid section comprising an upper and lower airfoil wall securedtogether.

13. An airfoil comprising a reinforcing spar having a plurality oflongitudinal passages, -a iller of plastic material contained in saidpassages, and a covering shell `of airfoil form enclosing said spar,said shell comprising identical sections arranged in side-:by-siderelation along the length of said spar, each said section comprising anupper and lower airfoil wall secured together.

14. An airfoil comprising a hollow, reinforcing spar, a plastic ller ofcured, fiberglass roving contained in said spar, and a covering 4mantleof complete airfoil Kform enclosing said spar, said mantle constitutingsubstantially the total structure of said airfoil, other than said spar,and comprising identical sections arranged in side-byside relation alongthe length of said spar, each said section comprising identical upperand lower airfoil shells secured together, .and extending from theleading edge to the trailing edge `of the airfoil.

15. An airfoil comprising ya hollow, reinforcing spar, a solid plasticiller contained in said spar, and a covering mantle of complete airfoilform enclosing said spar, said mantle constituting substantially thetotal structure of said airfoil, other than said spar, and comprisingidentical sections arranged in side-by-side relation along the length ofsaid spar, each said section comprising identical upper and lowerairfoil shells secured together, and extending from the leading edge tothe trailin-g edge of the airfoil.

16. For use in an airfoil, a reinforcing spar comprising a series oftubular members tangentially attached together, and a filler of solidplastic material in said tubes and extending from one end Iof said sparto distances.

which increase progressively insuccessive spars.

17. For use in an airfoil, a reinforcing spar comprising a series oftubular members tangentially attached together, and a filler of solidplastic material extending from one end of said spar and terminating atdistances which differ in at least two of said tubes.

References Cited in the le of this patent UNITED STATES PATENTS McCauleyJuly 1, 1930 Bergen Nov. 6, 1945 Larsen May 21, 1946 Young OctA 14, 1952Haines et a1. Aug. 11, 1953 Sterling Sept. 22, 1953 Stanley Nov. 17,1953 Harness Oct. 1, 1957 Schliekelmann Mar. 25, 1958 Laskowitz Dec. 1,1959 8 Marchetti Oct. 4, 1960 Stuart Apr. 25, 1961 Warnken Sept. 19,1961 Hinds Apr. 3, 1962 FOREIGN PATENTS Germany Dec. 3, 1919 GermanyJuly 20, 1940 Germany Jan. 29, 1941 Great Britain Apr. 16, 1952 ItalyApr. 22, 1955 Australia Feb. V6, 1956 Germany Aug. 7, 1958 Germany Apr.28,1960

17. FOR USE IN AN AIRFOIL, A REINFORCING SPAR COMPRISING A SERIES OFTUBULAR MEMBERS TANGENTIALLY ATTACHED TOGETHER, AND A FILLER OF SOLIDPLASTIC MATERIAL EXTENDING FROM ONE END OF SAID SPAR AND TERMINIATING ATDISTANCES WHICH DIFFER IN AT LEAST TWO OF SAID TUBES.